The present invention relates to a light radiator to be used in the cultivation of fish capable of receiving light energy transmitted through a fiber optic cable and for effectively radiating the same into water in order to produce algae and like plants for feeding and thereby raising fish.
In recent years, in relation to the necessity for saving energy, the effective utilization of solar energy has been actively studied and developed in various fields. The most effective utilization of solar energy is realized when it is used as light energy without being converted into thermal energy or electrical energy. From this point of view the present applicant has proposed various methods and systems for introducing solar rays focused by means of a lens system or the like into a fiber optic cable and to transmit the same therethrough to wherever the light is needed for illumination.
In any fish farm there is a great demand for zooplankton which eats algae to propagate itself. To effectively grow the algae it is necessary to properly supply the algae with sunlight and carbon dioxide. Generally, when algae increases and densely gathers, it may obstruct the light thereby preventing further propagation of the zooplankton.
The present applicant previously proposed a light radiator which is suitable for use in a chlorella culturing plant. An input end of the fiber optic cable is connected to a solar ray collecting device previously proposed by the present applicant, the device being intended to focus solar rays through a lens or the like and for introducing the focused solar rays into a fiber optic cable through which said solar rays are transmitted to wherever the light is needed. The solar rays collected by the above-mentioned solar ray collecting device are delivered through the fiber optic cable to a light-radiating device.
A light groove is spirally cut on the surface of the light guide's body. The light rays transmitted through the optic cable are introduced into the light guide and the light rays introduced into the light guide are reflected on the grooved portion and effectively radiated therefrom. In this case a substantially uniform radiation of the light from the whole body of the light guide may be achieved if the spiral groove is made in such a way that the spiral pitch gradually becomes narrow in the direction of the light being guided. Furthermore, when a reflecting plate or the like is placed at the end face of the light guide, the light reflected by the reflecting plate enters back into the light guide and is radiated therefrom. Furthermore, the light guide may be used hermetically enclosed in a semi-transparent or a transparent container to protect the light guide from being damaged by any other object. When the light guide, thus protected in the container, is used in water as a light source, its surface can always be prevented from a kind of fur forming on its surface and the radiation can be spread out more uniformly through the transparent container.
Another light-radiating device previously proposed by the present applicant has a light diffuser and a transparent or semi-transparent container.
The transparent or semi-transparent closed container is placed in water and the light rays transmitted through the fiber optic cable are diffused by the light diffuser and the diffused light rays are radiated into the water through the transparent or semi-transparent wall of the closed container. Consequently, algae may grow on the outer surface of the closed container and fish will gather around the closed container being attracted by the radiated light they and will eat the algae on the container's surface. The above-mentioned underwater light-radiating device is to be placed in water for cultivating aquatic plants and animals but when it is submerged deeply and, if its closed container is made of a plastic material that has thin walls, said container may be crushed by the increased water pressure thereby defeating the intended purpose.